[changelog] Add changelog for v1.0.2

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Protected files: CHANGELOG.md

Adds the CHANGELOG.md entry for the v1.0.2 stable release.

Changes covered (8 user-facing):

• 2 highlighted features: opt-in session memory, defer parameter for tool definitions
• 4 other improvements/features: OTLP protocol option, ModelBilling.tokenPrices, graceful runtime shutdown, Go context-aware JSON-RPC
• 2 bugfixes: Python sub-millisecond duration rounding, Rust docs.rs build skip
• 4 new contributors noted

Generated by Release Changelog Generator · sonnet46 1.8M · ◷

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Protected files were modified in this pull request and require manual scrutiny before merge.

Please verify that each protected-file change is intentional, policy-compliant, and safe:

• Protected files: CHANGELOG.md